1. Field of the Invention
This invention relates to gas turbine combustors and more specifically to a method of operating such a gas turbine so as to reduce emissions of nitrous oxides.
2. Description of Related Art
In an effort to reduce the amount of pollution emissions from gas-powered turbines, governmental agencies have enacted numerous regulations requiring reductions in the amount of emissions, especially nitrogen oxide (NOx) and carbon monoxide (CO). Lower combustion emissions can be attributed to a more efficient combustion process, with specific regard to fuel injectors and nozzles. Early combustion systems utilized diffusion type nozzles that produce a diffusion flame, which is a nozzle that injects fuel and air separately and mixing occurs by diffusion in the flame zone. Diffusion type nozzles produce high emissions due to the fact that the fuel and air burn stoichiometrically at high temperature to maintain adequate combustor stability and low combustion dynamics.
An enhancement in fuel injector technology over diffusion nozzles is the utilization of some form of premixing, such that the fuel and air mix prior to combustion to form a homogeneous mixture that burns at a lower temperature than a diffusion type flame and produces lower NOx emissions. Premixing can occur either internal to the fuel nozzle or external thereto, as long as it is upstream of the combustion zone. While combustion systems having premixing technology can lower emissions, the lower flame temperature associated with the premixing can cause flame stability and combustion dynamics issues.
What is needed is a system that can provide the benefits of flame stability and low combustion dynamics associated with the diffusion type nozzles with the low emissions benefits of the premix type nozzles.